Most electronic imagers adopt a design for capturing full color images with a single image sensor overlaid with a color filter array (CFA). A single image sensor can be a pixel array wherein each pixel includes a photo sensor which generates photoelectrons from photons. Additional circuitry next to each photo sensor converts the photoelectrons to a voltage. Extra circuitry on the pixel array may be included to convert the voltage to digital data. A color filter array on a pixel array enables each pixel or photo sensor to capture the intensity of light across a color spectrum. A microlens array is generally placed over the color filter array to focus the received light onto the photo sensors.
Color filter arrays and microlenses used in electronic imagers and sensors are often made of photoresist material. Different chemicals may be used to give the material desired property variations to be suitable for use as color filters.
Several factors related to a color filter array and a microlens influence the imaging quality in an electronic imager. First, certain mechanical and chemical properties of the photoresist material, such as hardness, chemical resistance, durability, resistance to humidity and other atmospheric stresses, determine the selection of a photoresist material. Chemical and physical changes may occur in the exposed areas of the photoresist layer. For example, chemical bonds may be formed or destroyed between some of adjacent photoresist color filters causing defects at the surface of the color filter array.
Next, the design of a pixel array coupled with a color filter array inevitably also suffers, due to physical characteristics of the optical and semiconductor components, from the problem of crosstalk between different pixel elements. Crosstalk, a phenomenon where photon or electron leakages cause an interaction between neighboring pixels, increases as the distances between pixels decreases. The nature of the crosstalk in image sensors has various origins: electron diffusion in the photo screen, insufficient optical separation of pixels or even electrical crosstalk in the readout sensor. The crosstalk in image sensors can desaturate colors and blur image details. Thus, when crosstalk occurs, resolution decreases in the image sensor, causing distortion in images produced by the sensor.